^(^6 



GENERAL CONDITIONS OF PLANT-LIFE. 



must have been clue to a mixture of the latter two. Olive Algae contain another 

 fundamental species, fucoxanthine. In many Fungi, and in the petals of flowers, occur 

 other more orange-coloured species, of which that in Pe%i%a aurantiaca is a good 

 example. Sorby adopted the name proposed by Kraus^ for a still more red orange- 

 coloured species; but what Kraus describes as phycoxanthine must have been a mixture 

 of this substance with fucoxanthine and lichnoxanthine. The difference between the 

 spectra of some of the above-named species will be better understood by means of the 

 following figure (476 r), which represents those of the solutions in carbon bisulphide. 



When these various substances are dissolved in benzol, their absorption-bands are all 

 equally raised towards the blue end, so that we appear to have a remarkable series of 

 very closely related substances. 



Lichnoxanthine group. — The colouring-matters belonging to this division are insoluble 

 in water, soluble in absolute alcohol, and sometimes also in carbon bisulphide. They all 

 give spectra without bands, and absorb more or less from the blue end. Some are 

 yellow, and others so red that they may be called lichnoerythrines. Lichnoxanthine 



Red end. 



Bine end. 



Phycoxanthine 



Peziza xanthine . . 



Orange xanthophyll 



Xanthophyll 



Yellow xanthopliyll . . 



Fig. 476 c— Spectra of the xanthophyll group compared. 



occurs in both the highest and lowest classes of plants, but the whole group is more 

 especially developed in Lichens and Fungi. It is not yet possible to say what part they 

 play in the economy of plants, and in some cases they are probably only products of the 

 oxidisation of chlorophyll and resins, from which they may be prepared artificially. 



We now come to a number of different groups, soluble in water but insoluble in 

 carbon bisulphide. 



Phycocyan and Phycoerythrine groups. — There are at least five distinct colouring- 

 matters included in these two groups, which differ from one another in many well-marked 

 particulars. The phycocyans are highly fluorescent, but the phycoerythrines little if at 

 all. They give remarkable spectra with one main absorption-band. Some are con- 

 nected with albuminous substances in much the same manner as the haemoglobin of 

 blood, being like it decomposed at exactly the same temperature as that at which 

 albumen coagulates, whilst the others appear to be associated with some different but 

 related substance. They are especially characteristic of red Algae, but also occur in a 

 few Lichens. 



* Chlorophyllfarbstoffe, p. 109, 



